利用UIImageJPEGRepresentation与UIGraphicsBeginImageContext进行图片压缩的简单比较

UIImage *image01 = [UIImage imageNamed:@"002.png"];//原图

NSData *dataOf02 =UIImageJPEGRepresentation(image01, 0.5);//压缩图片内容，不影响图片的size，得到一个原大小，但更模糊的图片。
UIImage *image02 = [UIImage imageWithData:dataOf02];//压缩图02

UIImage *image03 = [self makeThumbnailFromImage:image01 scale:0.5];//压缩图03
NSLog(@"001===%@",NSStringFromCGSize(image01.size));
NSLog(@"002===%@",NSStringFromCGSize(image02.size));
NSLog(@"003===%@",NSStringFromCGSize(image03.size));

NSData *data001 = UIImageJPEGRepresentation(image01, 1.0);
NSData *data002 = UIImageJPEGRepresentation(image02, 1.0);
NSData *data003 = UIImageJPEGRepresentation(image03, 1.0);

NSLog(@"002.lenght===%d",data001.length);
NSLog(@"002.lenght===%d",data002.length);
NSLog(@"003.lenght===%d",data003.length);

//看一下效果
UIImageView *imageView01 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, image01.size.width, image01.size.height)];
imageView01.image = image01;
[self.view addSubview:imageView01];

UIImageView *imageView02 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, image02.size.width, image02.size.height)];
imageView02.image = image02;
[self.view addSubview:imageView02];

UIImageView *imageView03 = [[UIImageView alloc] initWithFrame:CGRectMake(0, 200, image03.size.width, image03.size.height)];
imageView03.image = image03;
[self.view addSubview:imageView03];

//手动实现图片压缩，可以写到分类里，封装成常用方法。按照大小进行比例压缩，改变了图片的size。
- (UIImage *)makeThumbnailFromImage:(UIImage *)srcImage scale:(double)imageScale {
    UIImage *thumbnail = nil;
    CGSize imageSize = CGSizeMake(srcImage.size.width * imageScale, srcImage.size.height * imageScale);
    if (srcImage.size.width != imageSize.width || srcImage.size.height != imageSize.height)
    {
        UIGraphicsBeginImageContext(imageSize);
        CGRect imageRect = CGRectMake(0.0, 0.0, imageSize.width, imageSize.height);
        [srcImage drawInRect:imageRect];
        thumbnail = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }
    else
    {
        thumbnail = srcImage;
    }
    return thumbnail;
}